Molybdenum white iron casting



' Patented Sept. 10, 1935 UNITED STATES MOLYBDENUM WHITE IRON CASTING Carl M. Loeb, Jr., New York, N. Y., assignor to Climax Molybdenum Company, New York, N. Y., a corporation of Delaware No Drawing. Application May 19, 1933. Serial No. 671,905

6 Claims. (01. 75-1) ,The present invention relates to novel and improved white iron castings, cast from a molybdenum iron alloy, which are particularly adapted to withstand abrasion and are extremely tough and hard.

Objects and advantages of the invention will be set forth in part hereinafter and in .part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the features of novelty pointedv out in the appended claims.

The invention has for its object the provision of improved cast iron rolls of white iron, and castings in other shapes to be subjected to extreme wear, which are hard and tough, are extremely durable and will harden on working. The invention further provides castings of a white molybdenum iron alloy which can be sand-cast and may be used for many purposes for which chilled castings have heretofore been necessary.

In accordance with the present invention, the castings are formed from an alloy having as its essential ingredients the following elements: Iron, carbon, silicon, molybdenum and manganese, which may also contain, if desired, other elements, such as chromium and/or nickel. The carbon-content of the alloys of the present invention is preferably fairly high in order to obtain the desired hardness-while the silicon is kept as low as is permitted by the methods of casting, and the manganese content is determined largely by the amount of silicon employed. The percentage of molybdenum contained in the final casting is quite high; and is dependent upon the amount of silicon. If a. large amount of silicon is present, the amount of molybdenum used must be considerably increased. Molybdenum increases the toughness of the castings, as well as their hardness and resistance to wear. Chromium may be added in small amounts where some brittleness is,not objectionable and it serves to harden the carbides, while nickel is used only 'in case the castings are tobe chilled, and then only for the production of castings having relatively soft centers. When nickel is present in sand castings, the silicon content must be kept low in order to retain the desired hardness and structure of the castings throughout. In. general, it is found that molybdenum-alloy rolls in accordance with the present invention and having a. hardness of 600 Brinell, will wear better than nickel alloyrolls having a hardness of 700 Brinell.

The castings of the presentinvention are suitable for abrasive parts such as cement mill rolls and shells, coal pulve'rizers and ore crushing rollers. The castings of the present invention are also well suited to use as rolls for the cold rolling and finishing of various parts where high hardness accompanied byextreme toughness is 5 necessary in order to form a permanent mooth hard surface. These castings may be'fo ed by sand casting, or, if desired, may be chill-c t.

In carrying out the present invention, t e molybdenum effects the formation of a white iron 10 having a matrix of sorbite, troostite. martensite, austenite or combinations thereof within a network of carbides. The molybdenum gives the castings an inherent toughness, also rendering them work hardening. Furthermore, the cast- 15. "ings are much more easily cast than a material of similar structure containing a; high nickel content.

In accordance with the present invention, the castings are preferably formed from an alloy 2 containing from 3.50 to 4.00% carbon, 0.20 to 1.00% silicon, 1.00 to 1.75%. manganese, a trace] to 1.50% chromium and 3.00% to 4.00% molybdenum, while sulfur and phosphorus are kept to low values. The silicon is preferably kept under' 1%, and is as low as is permitted by the methods of casting, considering the shrinkage of the metal and its wildness but in certain cases may be as high as 2.0%. If an austenitic structure is desired, the silicon must be maintained quite low. \Manganese may vary from a trace to 2.0% and is used in place of some of the silicon k as it is better to kill the heat of the metal being cas't because it does not interfere with the structure as does silicon. The amount of chromium is determined by the hardness desired in the carbides, and up to 5.0% may be used where brittleness is not especially to be avoided. The amount of molybdenum employed may be often as low as 2.0%, and if the silicon is maintained 40 at a very low value, the molybdenum may be as low as 1.0%. However, with 2.0% silicon as much as 6% molybdenum may be. required. In case the silicon is held at a low value, the molybdenum gives exceptional toughness and'wear resistance, and if the molybdenum content is raised it produces an austenitic structure in the alloy.

Nickel may be advantageously employed, up to 6.0%, in accordance with the present invention where it is desired to produce castings having soft. centers, and in these cams chilling is necessary to harden the outer surfaces of the castings. In other cases,.however, nickel is gen er'ally detrimental and necessitates lowering the silicon content or the alloy.

The following specific examples of the composition of castings produced in accordance with the present invention, may be cited:

. Percent Total carbon 3.5

Silicon 0.9

Manganese 1.4

Chromium 1.0

Molybdenum 3.3

When chill-cast, the castings of this composition had a hardness of 578 Brinell on the chilled face and 652 Brinell on' the face opposite the chilled face. When sand-cast, this alloy produced castings having a hardness of 600 Brinell.

Percent Total carbon 3.5

Silicon 0.9

Manganese 1.4 Chromium 1.2

Molybdenum 3.9

Similar castings of this composition when sandcast had a hardness of 600 Brinell, and when chill-cast had a hardness of 683 Brinell on the chilled face as well as on the opposite face.

Percent Total carbon 3.6

Silicon 1.0

Manganese 1.4 Chromium 0.8 Molybdenum 2.5

Similar castings of this composition when sandcast had a hardness of 552 Brinell, and when chill-cast had a hardness of 555 on the chilledface and 600 on the face opposite the chilled face.

Percent Total carbon 3.2

Silicon 0.9 Manganese 1.4 Chromium 0.7 Molybdenum 2.4 Nickel 3.5

Such castings containing nickel had a hardness of only 364 when cast in sand, and when chilloast had a hardness of 627 on the chilled face and 364 on the face opposite the chilled face.

Castings produced in accordance with the present invention are extremely tough and. it is possible to peen or hammer down the corners of a casting without chipping, even when the hardness is over 600 Brinell. This property tends to eliminate premature breakage, and is in contradistinction to the brittleness of similar castings of nickel-iron alloys which is often so great as to cause breakage in transportation.

The production of the castings of the present invention is not limited to any particular method of melting, and the alloy may be melted in a' cupola, open hearth, air or electric furnace.

The castings produced in accordance with the present invention appear to have a relatively thick outer layer of martensite which is hard and surrounds a softer layer of troostite, and there is no tendency to graphitize at the centerof the casting. When chill-cast, the castings show a deep austenitic layer of metal, which is workhardenable, surrounding the layers of martensite and troostite.

The invention in its broader aspects is not lim ited to the specific compositions, steps and other details described, but departures may be made therefrom within the scope of the accompanying claimswithout departing from the principles of the invention and without sacrificing its chief advantages.

What I claim is:

1. A white iron casting cast from an alloy having as its essential ingredients the following elements: carbon 3.00 to 4.00%; silicon, 0.20 to 1.00%; manganese, 1.00 to 1.75%; chromium, in

effective amounts up to 1.50%; molybdenum, 2.25 to 4.00%; the balance being substantially all iron; and, the silicon content being sufficiently low with reference to the molybdenum content to form white iron.

2. A white iron casting cast from an alloy having as its essential ingredients the following elements: carbon, 3.50 to 4.00%; silicon, 0.20 to manganese, 1.00 to 1.75%; chromium, trace to 1.50%; molybdenum, 3.00 to 4.00%; the balance being substantially all iron; and the silicon content being sufficiently low with reference to the molybdenum content to form white iron.

3. A white iron casting cast from an alloy having as its essential ingredients the following elements, and in approximately the following amounts: carbon, 3.5%; silicon, 0.9%; manganese, 1.4%; molybdenum, 3.9%; chromium, 1.2%; the balance being substantially all iron.

4. A white iron sand casting having substantially the same hardness on its surface as on a chilled face and cast from an alloy having as its essential ingredients the following elements and in approximately the following amounts: carbon, 2.5 to 4.0%; silicon, 0.2 to 1.0%; manganese, 0.5 to 2.0%; molybdenum, 2.25 to 5.0%; chromium, in effective amounts up to 5.0%; and substantially free of nickel; the balance being substantially all iron; and, the silicon content being surficiently low with reference to'the molybdenum content to form white iron.

5. An alloy for the production of white iron castings having substantially the same hardness when cast in sand as when cast against a chill, 0

and having as its essential ingredients the follow ing elements: carbon, 2.5 to 4.0%; silicon, 0.2 to 1.0%; manganese, 0.5 to 2.0%; molybdenum,

' 2.25 to 5.0%; chromium, in effective amounts up to 5.0%; and substantially nickel free; the balance being substantially all iron; and, the silicon content being s'ufliciently low with reference lowing elements: carbon, 3.5%; silicon, 0.9%; manganese, 1.4%; molybdenum, 3.3%; chromium,

1.0%; and substantially free of nickel; the balance being substantially all iron.

CARL M. LOEB, JR. 

